The present invention relates to die assemblies of the cross-head type for applying coating materials to a filamentary member, e.g., plastic insulation to electrical wires. More specifically, the invention relates to novel and improved co-extrusion, cross-head die apparatus for simultaneously applying two layers of coating materials, i.e., an inner and an outer layer, to a filamentary member as it is moved longitudinally through the apparatus.
Cross-head die assemblies, such as those disclosed in U.S. Pat. Nos. 5,031,568 and 5,316,583 of the present inventor, include a body portion having a through, axial bore communicating with a radial bore. A tip member, having a through bore for establishing the path of travel of the filamentary member, is supported in the body axial bore by a tip holder, also referred to as a core tube. External surfaces on the tip and holder cooperate with internal surfaces on the die elements to define a flow path for the coating material, which is heated in order to be in a flowable state. The flow path leads to a die orifice through which the filamentary member and coating material pass as the coating layer is applied.
It is sometimes necessary to apply two layers of coating material, one in covering relation to the other, to electrical wires, or the like. This may be accomplished by providing in the body portion two radial bores, through which sources of the two coating materials communicate at different locations within the axial bore. It is difficult, however, to ensure proper flow of the two materials through the die apparatus, providing the necessary symmetrical, coaxial coating layers.
It is a principal object of the present invention to provide cross-head die apparatus for applying inner and outer layers of coating materials to a filamentary member in a unique manner, resulting in superior, double-layered coatings.
Another object is to provide co-extrusion, cross-head die apparatus which simplifies and facilitates the application of two, superposed layers of coating materials to a filamentary member.
Other objects will in part be obvious and will in part appear hereinafter.